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deprecate concatenating [...] #7998

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nolta
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@nolta nolta commented Aug 13, 2014 

julia> [1:2, 3]
WARNING: [a,b] concatenation is deprecated; use [a;b] instead
3-element Array{Int64,1}:
 1
 2
 3

julia> [1:2]
WARNING: [a] concatenation is deprecated; use [a;] instead
2-element Array{Int64,1}:
 1
 2

ref #2488, #3737, #7941

@kmsquire
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+1.

Perhaps suggest [a...] for the second case?

On Wed, Aug 13, 2014 at 2:35 PM, Mike Nolta notifications@github.com
wrote:

julia> [1:2, 3]WARNING: [a,b] concatenation is deprecated; use [a;b] instead3-element Array{Int64,1}: 1 2 3
julia> [1:2]WARNING: [a] concatenation is deprecated; use [a;] instead2-element Array{Int64,1}: 1 2

ref #2488 #2488, #3737
#3737, #7941

#7941

You can merge this Pull Request by running

git pull https://github.com/JuliaLang/julia mn/sanecat

Or view, comment on, or merge it at:

#7998
Commit Summary

  • make vcats explicit
  • deprecate concatenating [a,b,...] and T[a,b,...]

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Patch Links:

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#7998.

@StefanKarpinski
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I really just want a different operator altogether for array concatenation. Not sure what though.

@JeffBezanson
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If {} used its arguments to determine the array element type, it would make sense for [] to be concatenating and {} not. Or the other way around, though that's a more dramatic change.

Another advantage of switching them ({} concatenates, [] doesn't) is that both T[...] and [...] would just be "vector constructors". T{...} is taken by types, but that's ok because specifying an element type for the result of a concatenation is a bit odd and doesn't seem to be needed in practice.

@kmsquire
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+1 to using {} for concatenation... although that is a very breaking change, since that is one of the few ways to avoid concatenation right now. ;-/

@ViralBShah
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+1 for this change. I really would not want to break the concatenation operator.

@JeffBezanson
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Something that's not satisfying here is that if you want [a b;c d], but have it not concatenate, you have to use {a b; c d} (which could be changed to use an element type other than Any). This then becomes the only use for {}, which seems like a bit of a waste.

We would be better off having one always concatenate, and the other never. Or add something like Stefan's |a b| proposal, and reclaim {} for something else.

@nolta nolta closed this Aug 20, 2014
@nolta nolta deleted the mn/sanecat branch May 8, 2015 20:23
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5 participants
@nolta @kmsquire @StefanKarpinski @JeffBezanson @ViralBShah